Color photographic elements are conventionally formed with superimposed blue, green, and red recording layer units coated on a support. The blue, green, and red recording layer units contain radiation-sensitive silver halide emulsions that form a latent image in response to blue, green, and red light, respectively. Additionally, the blue recording layer unit contains a yellow dye-forming coupler, the green recording layer unit contains a magenta dye-forming coupler, and the red recording layer unit contains a cyan dye-forming coupler.
Following imagewise exposure, a negative working photographic element is processed in a color developer that contains a color developing agent that is oxidized while selectively reducing to silver the latent image bearing silver halide grains. The oxidized color developing agent then reacts with the dye-forming coupler in the vicinity of the developed grains to produce an image dye. Yellow (blue-absorbing), magenta (green-absorbing) and cyan (red-absorbing) image dyes are formed in the blue, green, and red recording layer units, respectively. Subsequently the element is bleached (i.e., developed silver is converted back to silver halide) to eliminate neutral density attributable to developed silver and then fixed (i.e., silver halide is removed) to provide stability during subsequent room light handling.
When processing is conducted as noted above, negative dye images are produced. To produce corresponding positive dye images, and hence, to produce a visual approximation of the hues of the subject photographed, white light is typically passed through the color negative image to expose a second color photographic material having blue, green, and red recording layer units as described above, usually coated on a white reflective support. The second element is commonly referred to as a color print element. Processing of the color print element as described above produces a viewable positive image that approximates that of the subject originally photographed.
A positive working color photographic element is first developed in a black-and-white developer where the exposed crystals are selectively reduced to metallic silver. The unexposed silver is then fogged and reduced by a chromogenic color developer in a subsequent step to generate cyan, magenta, and yellow image dyes. The film is further bleached and fixed as with the negative working film. The positive working film thus forms dyes in the unexposed areas and renders a positive image of the scene, directly.
A problem with the accuracy of color reproduction delayed the commercial introduction of color negative elements. In color negative imaging, two dye image-forming coupler containing elements, a camera speed image capture and storage element and an image display, i.e. print element, are sequentially exposed and processed to arrive at a viewable positive image. Since the color negative element cascades its color errors forward to the color print element, the cumulative error in the final print is unacceptably large, absent some form of color correction. Even in color reversal materials which employ just one set of image dyes, color correction for the unwanted absorption of the imperfect image dyes is required to produce acceptable image color fidelity for direct viewing.
Color correction means, for color negative or color reversal elements, have relied on imagewise interlayer development modification effects during wet chemical processing called interlayer interimage effects. In the case of color negative elements, these effects are most commonly achieved with development inhibitor releasing (DIR) couplers that imagewise release development inhibitors to reduce the extent of development of the receiving silver halide grains, and with colored masking couplers. In the case of color reversal elements, these effects are usually achieved through imagewise interlayer silver halide emulsion development inhibition during the first black-and-white development, and possibly with DIR couplers during the second color development step.
Alternatively, instead of optical print-through exposure to create a color print, the color negative or color reversal element can be scanned to record the blue, green, and red densities in each picture element (pixel) of the exposed area. The color correction that is normally achieved by chemical interlayer interimage effects can be achieved by electronically manipulating stored image information as its image-bearing signal. One example of electronic color correction produced by scanning a processed photographic recording material and manipulating the resultant image-bearing electronic signals to achieve improved color rendition can be found in the KODAK Photo CD.TM. Imaging Workstation system. In addition, optical printing by passing light through the processed photographic recording material to expose a second light-sensitive material is no longer necessary. The light exposures necessary to write the color-corrected output onto a suitable display material such as silver halide color paper exposed by red, green, and blue light emitting lasers can be calculated and those device-dependent writing instructions can be transmitted to such alternate printers as their code values (specific instructions for producing the correct color hue and image dye amount). Other means of electronic printing include thermal dye transfer material, color electrophotographic media, or a three color cathode ray tube monitor.
It has been found unexpectedly that different or larger color corrections can be managed by electronic color correction than can be achieved through chemical interlayer interimage effects in color negative or color reversal films. This enhanced capability allows the possibility of producing better colorimetric matches between the original scene color content and the rendered image reproduction. In order to accomplish improved color reproduction, more accurate photographic recording material spectral sensitivity is required. In particular, the spectral sensitivity of a film optimally designed for scanning and electronic color correction must more closely approach that of the human visual system. To accurately record colors the way the human eye perceives them, a recording element must have spectral sensitivities that are linear transformations of the blue, green, and red cone responses of the human eye. Such linear transformations are known as color matching functions. Color matching functions for any set of real primary stimuli must have negative portions. Within the realm of known photographic mechanisms, it is not possible to produce a photographic element having spectral sensitivities whose response is negative.
Examples of spectral sensitivities that approximate color matching functions are those of MacAdam (Pearson and Yule, J. Color Appearance, 2, 30 (1973). Giorgianni et al, U.S. Pat. No. 5,582,961 and U.S. Pat. No. 5,609,978, the disclosures of which are herein incorporated by reference, describe related spectral sensitivities applied to non-tabular emulsions in color reversal film elements capable of forming image representations that correspond more closely to the calorimetric values of the original scene upon scanning and electronic conversion. A characteristic of these color matching functions is a broad response for the red recording layer unit that has significant sensitivity at wavelengths between about 530 nm and 640 nm. This type of response function closely resembles the green-red response of the human eye and visual system.
The red sensitivity of a multilayer film element is determined by the light absorption profile of the silver halide emulsions in the red sensitive layer unit attenuated by any light absorbing materials that lie above it in the top layers of the film, such as ultraviolet filter dyes, Lippmann emulsions, yellow filter layers, the blue sensitive emulsions, the yellow and magenta colored masking couplers in color negative films, and of course the green sensitive emulsions themselves. The light absorption of the emulsions used in the red sensitive layer unit is in turn determined by the composite absorption of the specific combination of spectral sensitizing dyes adsorbed to the surface of the silver halide crystals, since silver halide emulsions only have native (intrinsic) sensitivity to blue light. Red sensitive emulsions used in the red recording layer unit that are commonly found in the art are observed to employ two or three red sensitizing dyes, and they typically peak in dyed absorptance from about 600 nm to about 660 nm. Broad light absorptance to produce color reproduction accuracy in accord with human visual sensitivity was not sought.
Sasaki in U.S. Pat. No. 5,169,746 employs a blend of four spectral sensitizing dyes applied to a tabular grain silver iodobromide emulsion to obtain increased half-peak bandwidth, but green-red sensitivity is not provided since the maximum absorptance and sensitivity of such emulsions is more bathochromic than 600 nm. Ezaki et al U.S. Pat. No. 5,258,273 likewise produces broad half-peak bandwidth red sensitive emulsions using four spectral sensitizing dyes, but fails to achieve green-red sensitivity as the maximum emulsion response occurs at greater than 600 nm. Fukazawa et al in U.S. Pat. No. 5,180,657 demonstrates green-red sensitivity with a peak dyed emulsion response at about 590 nm, but only three spectral sensitizing dyes were used and consequently inadequate half-peak absorption bandwidth was achieved to provide color matching performance to mimic the human visual response. Fukazawa et al in European Patent Application EP 0 434 044 A1 uses as many as three spectral sensitizing dyes concurrently with a silver iodobromide emulsion to achieve spectral sensitivity as hypsochromic as about 580 nm, but low half-peak bandwidth resulted and more than one local maximum sensitivity was apparent. Shiba et al in U.S. Pat. No. 5,037,728 reveal the use of up to four dyes in combination; however the maximum sensitivity of the dyed emulsion falls at about 620 nm despite broad half-peak bandwidth performance. Yamada et al in U.S. Pat. No. 5,252,444 achieves high dyed emulsion half-peak bandwidth with merely two spectral sensitizing dyes, but continuous spectral response was absent with two local maximum sensitivities and principal response falling above 620 nm. Ohtani et al in U.S. Pat. No. 5,200,308 provide an emulsion employing three sensitizing dyes simultaneously to achieve high half-peak bandwidth, but the maximum absorption and sensitivity appear around 640 nm indicative of red, not green-red sensitivity.
Giorgianni et al '961 and '978 demonstrate a conventional, low aspect ratio silver iodobromide emulsion dyed with three J-aggregating cyanine dyes; green-red sensitivity with a high overall half-peak bandwidth was achieved, but the dyed emulsion disclosed produced multiple local absorption maxima again compromising the continuity of the green-red response. These maxima signify the lack of mixed aggregation of the sensitizing dyes, which has flawed the emulsion response with multiple discrete sensitivities. Their goal of significantly broad, unbroken red sensitivity that overlaps with green sensitivity to mimic the human visual system for improved color capture accuracy and reduced mixed illuminant sensitivity was not satisfied.